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Abstract

We introduce an all-optical, format transparent hash code generator and a hash comparator for data packets verification with low latency at high baudrate. The device is reconfigurable and able to generate hash codes based on arbitrary functions and perform the comparison directly in the optical domain. Hash codes are calculated with custom interferometric circuits implemented with a Fourier domain optical processor. A novel nonlinear scheme featuring multiple four-wave mixing processes in a single waveguide is implemented for simultaneous phase and amplitude comparison of the hash codes before and after transmission. We demonstrate the technique with single polarisation BPSK and QPSK signals up to a data rate of 80 Gb/s.

Figures (12)

Principle of the all-optical hash key verified link. Hash codes are generated inside the transmitter and communicated through the network along with the data in an adjacent channel. At the receiver side, hash codes are recalculated from the data channel and compared to the transmitted hash. On the diagram, red components indicate optical devices and green the electrical domain.

Principle of the all optical coherent signal comparator. Left: hash signals to be compared are copropagated with pumps through a third-order nonlinear medium after relative phase and amplitude adjustment. Inset: Two simultaneous FWM-based wavelength shifting processes occur inside the nonlinear medium. Two pumps with half the frequency spacing of the hash signals bring both idlers to the same wavelength. Initial configuration of the signals with opposite phases (represented by arrows facing in opposite directions) causes the idlers to interfere destructively so as to cancel the total idler product when both hash are equal. Mismatch between hash codes causes an idler spike. Bandpass filtering (BPF) of the total idler extracts the error signal.

Hash code generation by Fourier domain optical processing. Left: power and phase transfer
functions programmed in the FD-POP. The spectral profiles applied to the data signal reproduce the
characteristics of a multipath interferometric circuit (MIC) coherently adding successive bits.
Blue, green and red traces correspond to different MIC configurations. The other channel is left
untouched through a bandpass filter transfer function. Right: equivalent MIC implemented in the
FD-POP.

Experimental intensity plots of the hash codes for BPSK (first and second columns) and QPSK
(third and fourth columns) signals. Information encoded in the phase of the hash signals is not
represented. Time traces (top row) and eye diagrams (bottom) of the 64 bits patterns are measured
with a sampling oscilloscope. Blues traces show simulation results for the corresponding bit
patterns.

Experimental optical spectrum at the HNLF output. Insert: the total idler cancels out for
identical hash and not if they differ. Solid: both hash signals equal ; dotted: one error every 512
symbols ; dashed: hash functions different for both signals.

Variation of the signal generator to create localized errors in a BPSK signal. The two replicate
channels are split onto two arms, one being affected by a π phase shift of
one bit period every 512 symbols. Both paths are recombined into the first FD-POP acting as a
wavelength selective switch. PM: phase modulator ; PS: phase shifter.

Time traces of the error signal after bandpass filtering of the idler in the case of a single
error. Top: Idler channel filtered out. Bottom left: both hash signals equal (no error). Bottom
right: a single error causes a spike in the error signal.

Hash key verified link of 20.72 km. Left: composition of the link. Right: Idler channel filtered out in case of both equal (green) and different (black) hash function definitions. The corresponding eye diagrams show the error signal in the time domain.

Theoretical and experimental inaccuracy in the hash subtraction as functions of the phase perturbation between the two hash signals. The measurement was realized by feeding two equal signals in the coherent comparator and sweeping over their relative phase.